combining weight

combining weight, the proportion (by weight) in which a chemical element combines with other elements to form compounds. The determination of combining weights was a very important part of early chemical endeavor. The atomic theory of John Dalton (see atom) was based in part on his determinations of combining weights, which he called atomic weights. Combining weights were usually measured by early chemists on a scale in which hydrogen had a combining weight of 1. See equivalent weight.